slack bridge: Remove support for the legacy RTM API.

This is an optional commit that drops support running
the Slack Bridge using the legacy RTM API. The reasoning
for removing backwards compitability is because the user
can just use the older version of pyton-zulip-api.

zulip/integrations/bridge_with_slack/run-slack-bridge

@@ -8,13 +8,11 @@ import traceback
 from typing import Any, Callable, Dict, Optional, Tuple
 
 import bridge_with_slack_config
-from slack_sdk.rtm_v2 import RTMClient
 from slack_sdk.web.client import WebClient
 
 import zulip
 
 # change these templates to change the format of displayed message
-ZULIP_MESSAGE_TEMPLATE = "**{username}**: {message}"
 SLACK_MESSAGE_TEMPLATE = "<{username}> {message}"
 
 StreamTopicT = Tuple[str, str]
@@ -47,7 +45,6 @@ class SlackBridge:
         self.zulip_config = config["zulip"]
         self.slack_config = config["slack"]
 
-        self.slack_to_zulip_map: Dict[str, Dict[str, str]] = config["channel_mapping"]
         self.zulip_to_slack_map: Dict[StreamTopicT, str] = {
             (z["channel"], z["topic"]): s for s, z in config["channel_mapping"].items()
         }
@@ -65,8 +62,6 @@ class SlackBridge:
         # https://github.com/zulip/python-zulip-api/issues/761 is fixed.
         self.zulip_client_constructor = zulip_client_constructor
 
-        # slack-specific
-        self.slack_client = rtm
         # Spawn a non-websocket client for getting the users
         # list and for posting messages in Slack.
         self.slack_webclient = WebClient(token=self.slack_config["token"])
@@ -77,13 +72,6 @@ class SlackBridge:
             if w.startswith("@"):
                 zulip_msg["content"] = zulip_msg["content"].replace(w, "<" + w + ">")
 
-    def replace_slack_id_with_name(self, msg: Dict[str, Any]) -> None:
-        words = msg["text"].split(" ")
-        for w in words:
-            if w.startswith("<@") and w.endswith(">"):
-                _id = w[2:-1]
-                msg["text"] = msg["text"].replace(_id, self.slack_id_to_name[_id])
-
     def zulip_to_slack(self) -> Callable[[Dict[str, Any]], None]:
         def _zulip_to_slack(msg: Dict[str, Any]) -> None:
             slack_channel = get_slack_channel_for_zulip_message(
@@ -102,36 +90,6 @@ class SlackBridge:
 
         return _zulip_to_slack
 
-    def run_slack_listener(self) -> None:
-        members = self.slack_webclient.users_list()["members"]
-        # See also https://api.slack.com/changelog/2017-09-the-one-about-usernames
-        self.slack_id_to_name: Dict[str, str] = {
-            u["id"]: u["profile"].get("display_name", u["profile"]["real_name"]) for u in members
-        }
-        self.slack_name_to_id = {v: k for k, v in self.slack_id_to_name.items()}
-
-        @rtm.on("message")
-        def slack_to_zulip(client: RTMClient, event: Dict[str, Any]) -> None:
-            if event["channel"] not in self.slack_to_zulip_map:
-                return
-            user_id = event["user"]
-            user = self.slack_id_to_name[user_id]
-            from_bot = user == self.slack_config["username"]
-            if from_bot:
-                return
-            self.replace_slack_id_with_name(event)
-            content = ZULIP_MESSAGE_TEMPLATE.format(username=user, message=event["text"])
-            zulip_endpoint = self.slack_to_zulip_map[event["channel"]]
-            msg_data = dict(
-                type="stream",
-                to=zulip_endpoint["channel"],
-                subject=zulip_endpoint["topic"],
-                content=content,
-            )
-            self.zulip_client_constructor().send_message(msg_data)
-
-        self.slack_client.start()
-
 
 if __name__ == "__main__":
     usage = """run-slack-bridge
@@ -142,9 +100,7 @@ if __name__ == "__main__":
 
     sys.path.append(os.path.join(os.path.dirname(__file__), ".."))
     parser = argparse.ArgumentParser(usage=usage)
-    parser.add_argument(
-        "--legacy", action="store_true", help="Run the bridge using the legacy Slack RTM API"
-    )
+
     args = parser.parse_args()
 
     config: Dict[str, Any] = bridge_with_slack_config.config
@@ -158,10 +114,6 @@ if __name__ == "__main__":
     print("Starting slack mirroring bot")
     print("MAKE SURE THE BOT IS SUBSCRIBED TO THE RELEVANT ZULIP STREAM(S) & SLACK CHANNEL(S)!")
 
-    # We have to define rtm outside of SlackBridge because the rtm variable is used as a method decorator.
-    # the RTM API is a legacy Slack SDK, we keep using them only to provide backwards compitability.
-    rtm = RTMClient(token=config["slack"]["token"])
-
     backoff = zulip.RandomExponentialBackoff(timeout_success_equivalent=300)
     while backoff.keep_going():
         try:
@@ -173,23 +125,11 @@ if __name__ == "__main__":
             print("Starting message handler on Zulip client")
             zp.start()
 
-            if args.legacy:
-                sp = threading.Thread(target=sb.run_slack_listener, args=())
-                print(
-                    "Warning! Running on legacy Slack SDK\n"
-                    "Starting message handler on Slack client"
-                )
-                sp.start()
-                sp.join()
-                zp.join()
-            else:
-                print(
-                    "Warning! if you haven't moved to the new Slack app,\n"
-                    "please run the script with the --legacy argument.\n"
-                    "Make sure your Slack Webhook integration is running\n"
-                    "to receive messages from Slack."
-                )
-                zp.join()
+            print(
+                "Make sure your Slack Webhook integration is running\n"
+                "to receive messages from Slack."
+            )
+            zp.join()
         except Exception:
             traceback.print_exc()
         backoff.fail()